Subject: [manet] RFC5444 packet sequence numbers and acknowledgement

From: "Rick Taylor" <[email-masked]>
Date: Wed, 30 Nov 2011 16:00:59 -0000

Hi,

I have been taking a close look at RFC5444 for use in MANET routing
protocols, using the OLSRv2 and DLEP drafts as usage guides and have a
query regarding acknowledgements.

DLEP in particular uses specific Message TLVs to acknowledge receipt of
messages, i.e. Neighbour Up --> Neighbour Up ACK.

What confuses me however is that RFC5444 packets can have a sequence
number, but there appears to be no guidance on the use of packet TLVs to
request or supply acknowledgement to the receipt of a packet?

Now I understand that message level acknowledgement is semantically
different from packet level, as in "I have not only received your
packet, but also understood your message and processed it", but I am
left wondering if there is a case for a generic "I have received your
packet and delivered its contents to the relevant protocol stacks"
packet TLV that can be added to any reply packets.

I also understand that some protocols do not care if some messages are
not delivered or delivered out of order, but sometimes protocols do
care, and is the correct approach to add matching message_ACK TLVs for
those messages, rather than adding a common mechanism that covers "One
or more of the messages in this packet require acknowledgement, please
respond"?

I don't want to open a huge discussion over selective ACKs, NACKs,
windowing, throttling, etc. as my gut reaction would be "send your
packets via a more reliable protocol", but in the case of one or two
messages of many within a protocol requiring acknowledgement, I feel
doubling-up message TLVs seems wasteful.

Regards,

Rick Taylor
Software Engineer, Mobile IP Node
Cassidian Systems